The present disclosure generally relates to an implant system for use in orthopaedic surgery. Specifically, the disclosure relates to an intramedullary nail for internal fixation of bone, such as a femur.
Femur fractures commonly occur in the femoral neck and the trochanteric regions. Typically, trochanteric and sub-trochanteric femur fractures are currently treated with an intramedullary nail having a transverse bore to receive a bone fastener, such as a femoral neck screw usually provided in the form of a lag screw. The intramedullary nail is fitted in the intramedullary canal of the femur and the lag screw passes through the transverse bore of the intramedullary nail, through the neck of the femur and into the femoral head.
The lag screw is designed to transfer the load of the femoral head into the nail shaft by bridging the fracture line to allow fast and secure fracture healing. Further, the lag screw is allowed to slide in the intramedullary nail in accordance with the sintering of the femoral fracture. Typically, a set screw is inserted into a bore of the intramedullary nail to prevent a rotation and an uncontrolled medial deviation of the lag screw.
The intramedullary nail may include a central cannulation along its longitudinal axis for receiving a surgical wire (guide wire), such as a Kirschner-wire. The surgical wire is inserted into the marrow cavity of the femur prior to the insertion of the intramedullary nail.
U.S. Pat. No. 5,176,681 A relates to an intramedullary intertrochanteric fracture fixation appliance and fitting device. The intramedullary fracture fixation appliance comprises an intramedullary nail having a transverse bore for receiving a femoral neck screw in the form of a lag screw. The proximal end of the intramedullary nail is provided with another bore extending co-axially through the nail and opening into the transverse bore. A set screw is located within the co-axial bore of the nail. The lower end of the set screw has a centrally arranged protrusion. When the set screw is in its final position, the central protrusion of the set screw engages in one of longitudinally extending grooves arranged on the shaft of the lag screw.
U.S. Pat. No. 6,835,197 relates to an intramedullary nail with a coupling mechanism. The coupling mechanism includes a body member and a flat prong laterally extending from the body member. Further, a short bolt for threadable engagement with a partially threaded channel that extends axially in the intramedullary nail is rotatably coupled to the body member. The body member further includes tabs, which are received in grooves of the channel, such that cooperation between the tabs and the grooves prevents rotation of the body member within the channel. When the body member is urged toward a lag screw inserted through a transverse bore of the intramedullary nail, the flat prong contacts a side surface of the lag screw and fills a void defined by the flat portion of the lag screw, such that the prong fits tightly in the space between the channel wall and the lag screw.
U.S. Pat. No. 6,648,889 B2 relates to an intramedullary nail with a bifurcated lock. Similar to the body member described in U.S. Pat. No. 6,835,197 B2, a sleeve lock includes two lateral locking tabs in the form of flat prongs and an anti-rotation tab engaging within a groove of a channel of the intramedullary nail. The locking tabs of the sleeve lock engage within locking slots of a sleeve which is arranged on the lag screw.
U.S. Pat. No. 6,406,477 B1 relates to an intramedullary nail having a set hole in its proximal portion. The proximal portion of the nail further has two transverse bores in which a lag screw and an auxiliary connector are to be located. Since the auxiliary connector extends through the nail at a location between a set screw screwed into the set hole of the intramedullary nail and the lag screw, a spacer for transmitting a clamping force is interposed between the set screw and the lag screw. The spacer includes a body and two apart legs laterally extending from the body. When the set screw is placed on the spacer in the set hole and is screwed into the set hole, the set screw pushes the entire spacer down and the lower ends of the legs engage within grooves of the lag screw. The auxiliary connector is positioned between the two legs of the spacer and is securely held by a central boss formed at the forward end of the set screw and inserted through an opening formed in the body of the spacer.
US 2006/0200160 A1 discloses a coupling arrangement between an intramedullary nail and a lag screw. A coupling assembly includes an engagement member and an engagement driver. The coupling assembly is received in a proximal portion of a bore of the intramedullary nail for engaging a portion of the lag screw that is located within a transverse bore of the intramedullary nail. The engagement driver is threadably coupled with the intramedullary bore of the nail and operates to move the engagement member between a disengaged position and an engaged position. The engagement member includes two engagement arms formed as flat prongs which can engage the lag screw when the engagement member is in the engaged position.
Further technological background can be found in EP 1 175 872 A2 (U.S. Pat. No. 6,046,477) and EP 1 547 534 A2 (U.S. Pat. No. 7,601,153).
The conventional intramedullary nails have several drawbacks. A set screw without a through hole cannot be preassembled with the intramedullary nail and thus has to be inserted into the intramedullary nail intraoperatively after removal of a guide wire. In this case, the insertion of the relatively small set screw into the shaft of the intramedullary nail is cumbersome. Soft tissue overlapping the opening at the proximal end of the nail may hinder the insertion of the set screw and the mutual engagement of the threads. Thus, the set screw may get stuck within the intramedullary nail and the operation time increases due to additional operation steps. Moreover, a set screw having one or more prongs cannot prevent an uncontrolled medial deviation of the lag screw. Hence, the construct of intramedullary nail, coupling assembly and lag screw inserted through the transverse bore of the intramedullary nail and into bone can therefore not provide a high mechanical load stability within the body of the patient. Additionally, using set screws with prongs requires a modification of the current lag screw shaft design providing longitudinal extending grooves in which a pin of the set screw can engage to guarantee a defined sliding of the lag screw within the intramedullary nail.